Exactly what Lin52 said. Tried all of the deselecting/selecting, tried deleting the thumbnail cache, applying to all files, changing default viewer, changing size of thumbnails.
None of it works.
Symptoms are that maybe 10% of thumbnails show as correct image, the balance are all the default viewer icon. The mix of good image to icon seems random, with no accounting for date of creation, type of file, size of file, etc.
The green task bar at the top of the explorer page s-l-o-w-l-y cranks to maybe 95%-ish green, but fails to complete the cycle regardless of how long it's left to complete it's task.
This sucks. Hard. Not being able to see the thousands of images I've created/saved to my PC makes it not worth having. Someone help?